Threats to Frogs

One third to one half of all ~6000 known amphibian species are threatened with extinction, with probably more than 120 species already likely to have been lost in recent years. Extinctions are hard to confirm though with many species ‘missing’ but unable to be called extinct until exhaustive surveys have been conducted.

Without ex situ intervention, 500 species are estimated to soon become extinct. 

So why are frogs species being threatened?

Human utilisation of land can break up the environment, leaving small fragments of suitable habitat which are separated by unsuitable land.  This makes it difficult for frogs to transverse the landscape between suitable patches. 

If fragmentation is severe, animals may not be able to disperse and reach suitable breeding sites, meaning they cannot reproduce.  This problem can be amplified by species having different habitat requirements for different life stages, as the need to move between patches can become even greater. 

Habitat change is thought to be affecting ~4000 amphibian species.

Compared to rates of decline from disease, habitat fragmentation can act more slowly, providing opportunity for countermeasures such as protecting and rehabilitating areas to be undertaken.  Natural habitat with a variety of habitat sub-types best for protecting biodiversity, including frogs.

Frogs are extremely sensitive to chemicals in their environment as they have a highly permeable skin that easily draws in water and whatever chemicals may be dissolved in that water.

Some of the impacts that chemicals can have are given in WWF Frogs in an Effluent Society  pdf

Atmospheric pollution can also affect frog populations through a variety of means, including effects from climate change, ozone thickness and the production of acid rain.  For example, one effect climate change can have is to affect the moistness of an environment, making once suitable habitat no longer suitable for a particular species. 

Chytridiomycosis is a disease that is increasingly found to be affecting amphibian populations around the world, with its effects being felt in every amphibian inhabited continent.  The disease is caused by a fungus, Batrachochytrium dendrobatidis, which infects the skin of amphibians making difficult for animals to absorb water and breathe, two functions that frogs use their skin for. 

The fungus requires a certain set of conditions in order to survive and spread, generally those found in cooler riparian habitats, but not all frog species have the same habitat requirements.  This variability in habitat needs means not all frog species will become infected with the disease in the wild, even those species that may be infected in the laboratory.  A few lucky species appear to be able to live with the infection, but this has consequences for other species which may be infected by these carriers.

Disease outbreaks can have sudden and dramatic effects on population numbers and in severe cases can lead to rapid extinction.